Share iPhone 3GS internet with iPhone 4S

Hello users,

This is my first question here.

I have an iPhone 3GS (iOS 6.1.6) and I want to share its internet connection (3G) by bluetooth with an iPhone 4S (iOS 8.1.3).

I have enabled Personal Hotspot on 3GS and bluetooh on booth but I can't see the 3GS connection in the bluetooth menu on the 4S.

Can this be done or is it there a limitation?

Thank you very much,